PORTLAND, ore. — The gunman who killed two people and himself in a shooting rampage at an Oregon mall was 22 years old and used a stolen rifle from someone he knew, authorities said Wednesday.

Jacob Tyler Roberts had armed himself with an AR-15 semiautomatic rifle and had several fully loaded magazines when he arrived at a Portland mall Tuesday, said Clackamas County Sheriff Craig Roberts.

The sheriff said the rifle jammed during the attack, but Roberts managed to get it working again. He later shot himself. Authorities don’t yet have a motive but don’t think he was targeting specific people.

Two people — a 54-year-old woman and a 45-year-old man — were killed. Another, Kristina Shevchenko, 15, was wounded and in serious condition Wednesday.

Roberts, wearing a hockey-style mask, parked his 1996 green Volkswagen Jetta in front of the second-floor entrance to Macy’s and walked through the store, into the mall and began firing randomly, police said.

He fatally shot Steven Mathew Forsyth of West Linn and Cindy Ann Yuille of Portland, the sheriff said.

Roberts then fled along a mall corridor and into a back hallway, down stairs and into a corner where police found him dead from an apparent self-inflicted gunshot, authorities said.

People at the mall were heroic in helping get shoppers out of the building, including medical personnel who rendered aid, Roberts said.

In response to previous mass shootings elsewhere, the first arriving officers were trained to form teams and go inside instead of waiting for SWAT. Employees at the mall also received training to handle such a situation.

“This could have been much, much worse,” Craig Roberts said.

The first 911 call came at 3:29 p.m. Tuesday and officers arrived a minute later. By 3:51 p.m., all the victims and the gunman and rifle had been found. Four SWAT teams spent hours clearing the 1.4 million square-foot mall, leaving shoppers and workers to hide in fear.

Roberts rented a basement room in a modest, single-story Portland home and hadn’t lived there long, said a neighbor, Bobbi Bates. Bates said she saw Roberts leave at 1:30 p.m. Tuesday wearing a dark jacket and jeans, carrying a guitar case.

Clackamas Town Center is one of the Portland area’s biggest and busiest malls, with 185 stores and a 20-screen movie theater.

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